May 31, 2013
LRO images from NASA/GSFC/Arizona State Univeristy
The images keep getting better but improvements in understanding are having a hard time keeping up. Since I first catalogued concentric craters (CC) in 1978 using Apollo and Lunar Orbiter photographs there were decades with little significant improvement in imaging, but now with the Lunar Reconnaissance Orbiter Cameras, uniform high and hyper resolution views exist of nearly the whole Moon. This LPOD features LRO views of a CC inside the Apollo Basin on the farside - it is No. 50 of my list. No. 50 is on the northern side of the basin, beyond the central mare, but perhaps in a area where older mare is covered with a veneer of highlands material or where there is a non-mare volcanism (i.e., not dark). The reason for suggesting this is that the bench regions between basin rims often seem to be filled with smooth plains, and like this area, be cut by rilles. In 1978 I suggested that the most likely origin for CCs was colonization of an impact crater by volcansim. This suggestion has been ignored and few subsequent studies have occurred. The most recent investigation by Trang and colleagues could not reach a definitive conclusion, but favored igneous intrusion. The LRO images, both WAC and NAC, give the best views yet of features we still can't explain.
21st Century Atlas chart F4.
Yesterday's LPOD: Perfect Circles
Tomorrow's LPOD: Gravity Man